Today, almost all mobile phones are equipped with a clock, including PDA's and other mobile communication devices, which also maintain calendaring, and, in some instances, EMail and browser functions. In some digital cellular/PCS systems, such as the IS-95/2000 CDMA system, the clock in a phone is synchronized to the precise local time (Coordinated Universal Time (UTC)+time zone) given by the base station to which the phone is currently communicating with. Once synchronized, the mobile station maintains the clock until the phone is turned off. As a result, users of such phones do not have to adjust the phone clocks while they are in a digital service coverage area.
However, if the mobile phone is powered up outside of a digital service coverage area, the mobile station may lose the current time, unless it is equipped with a battery-back-up real-time clock hardware (RTC). The RTC maintains the clock while the mobile phone is turned off, but requires extra physical space within the phone and increases the manufacturing costs. For a mobile phone without an RTC, applications that rely on the clock will not function when the current time is lost. For example, in such a case the “alarm clock” feature will miss the time at which it is supposed to give a visual/audible alert to the user.
In addition, because a RTC is normally driven by a low-cost crystal oscillator with only marginal accuracy, the mobile phone may not have a sufficiently accurate clock even if it is equipped with an RTC.
Some mobile phones provide the capability for users to set the current time manually. However, a user may not be aware of the need to set the phone clock manually, or may forget to set the time manually, and thereby not receive important clock-dependent information, or receive the information at an inappropriate time.
U.S. Patent Publication No. 20020116658 A1, of Yano, Published Aug. 22, 2002, for Terminal device and real-time clock control method therefor enabling preservation of clock/calendar information and high information readout speed, describes a method for clock/calendar information to be maintained reliably and correctly through the use of dual RTCs.
U.S. Pat. No. 6,282,431, to Konno, granted Aug. 28, 2001, for Time correcting method and portable remote telephone terminal in which time is corrected in accordance with such method, describes a time correcting method by receiving notifying information from a base station.
U.S. Patent Publication No. 20020098857 A1, of Ishii, published Jul. 25, 2002, for Clock for mobile phones, describes a method of managing time zone changes for mobile devices.
WO0079349, of Ostsjo et al., for Method and Apparatus for Real Time Clock Frequency Error Correction, published Dec. 28, 2000, describes a method of calibrating/correcting a phone's RTC.
WO0052847, of Persico, for Radiotelephone Timer, published Sep. 8, 2000, describes a programmable timer using a RTC, for setting unitary or repeatable clock events.
WO9814842, of LaSalle, for Synchronization of a Timepiece to a Reference Time, published Apr. 9, 1998, describes a method and apparatus for synchronizing a timepiece to a reference time, particularly when changing between daylight and standard time.